Process and system for austempering metal workpieces

Abstract

In a process and an apparatus for austempering, metal workpieces and optional tempering bodies are quenched in a quenching volume V of a quenching apparatus, in which the quenching volume V is flowed through by a cooling fluid, and the workpieces are tempered by thermal radiation of the tempering bodies, by thermal radiation of one or more heating elements arranged in the quenching apparatus, or by a thermal fluid in such a way that an average temperature T(t) of the workpieces follows a progression over time according to the relationship T ⁡ ( t ) = T 0 + T 1 [ 1 + tanh ⁡ ( - t τ ) ] where t is the time in seconds, 150° C.≤T 0 ≤250° C., 600° C.≤T 1 ≤820° C., 12 s≤τ≤24 s, 0 s≤t≤Γ and 180 s≤Γ≤240 s.

1 . A method of austempering metallic workpieces, comprising the steps of:
 arranging the workpieces on a batch carrier;   optionally arranging one or more tempering bodies on the batch carrier;   optionally arranging a metallic reference body on the batch carrier;   thermally or thermochemically treating the workpieces arranged on the batch carrier and optionally the tempering bodies and/or the reference body, where the workpieces are heated to a temperature of 750 to 1100° C.;   arranging the batch carrier together with the workpieces and optionally the tempering bodies and/or the reference body in a quench volume V of a quench apparatus;   quenching the workpieces and optionally the tempering bodies and/or the reference body, where
 (a) a cooling fluid is allowed to flow through the quench volume V, and 
 (b) the workpieces are tempered
 with thermal radiation from the tempering bodies, 
 with radiation from one or more heating elements disposed in the quench apparatus, or 
 with a heating fluid; 
 
   
       wherein an average temperature T(t) of the workpieces has a progression against time according to the relationship 
       
         
           
             
               
                 T 
                 ⁡ 
                 ( 
                 t 
                 ) 
               
               = 
               
                 
                   T 
                   0 
                 
                 + 
                 
                   
                     T 
                     1 
                   
                   [ 
                   
                     1 
                     + 
                     
                       tanh 
                       ⁡ 
                       ( 
                       
                         - 
                         
                           t 
                           τ 
                         
                       
                       ) 
                     
                   
                   ] 
                 
               
             
           
         
         where t denotes time in seconds, 150° C.≤T 0 ≤250° C., 600° C.≤T 1 ≤820° C., 12 s≤τ≤24 s, 0 s≤t≤Γ and 180 s≤Γ≤240 s. 
       
     
     
         2 . The method as claimed in  claim 1 , wherein the cooling fluid used is air, nitrogen, helium or hydrogen. 
     
     
         3 . The method as claimed in  claim 1 , wherein a pressure of the cooling fluid in the quench volume Vis 2 to 20 bar. 
     
     
         4 . The method as claimed in  claim 1 , wherein the heating fluid is steam at a temperature of 150 to 250° C. 
     
     
         5 . The method as claimed in  claim 1 , wherein the method further comprises measuring an average temperature T(t) of the workpieces or a temperature of the reference body during quenching. 
     
     
         6 . The method as claimed in  claim 1 , wherein the method further comprises controlling the volume flow rate (m 3 /s) of the cooling fluid through the quench volume V by electronic closed-loop control. 
     
     
         7 . The method as claimed in  claim 1 , wherein the method further comprises subjecting the power (kW) of the at least one heating element to electronic closed-loop control. 
     
     
         8 . The method as claimed in  claim 1 , wherein the method further comprises subjecting the volume flow rate (m 3 /s) of the heating fluid in the quench volume V to electronic closed-loop control. 
     
     
         9 . The method as claimed in  claim 1 , wherein the quench volume V has a size of 0.03 to 1 m 3 . 
     
     
         10 . A system for austempering metallic workpieces, comprising:
 one or more batch carriers for the storage of workpieces;   optionally one or more tempering bodies composed of a metallic material, graphite or carbon fiber-reinforced graphite (CFC);   optionally a reference body composed of a metallic material;   a furnace for the thermal or thermochemical treatment of workpieces disposed on one or more batch carriers and optionally tempering bodies and/or the reference body, where the furnace is designed and set up to heat the workpieces up to a temperature of 750 to 1100° C.; and   a quench apparatus comprising
 a quench chamber having a quench volume V for accommodation of one or more batch carriers comprising workpieces and optionally tempering bodies and/or the reference body; 
 a vessel for cooling fluid and a fluid drive controllable by electronic closed-loop control for the flow of cooling fluid through the quench volume V; 
 one or more temperature sensors for the measurement of a temperature T(t) of the workpieces or a temperature of the reference body; 
 optionally one or more heating elements controllable by electronic closed-loop control; 
 optionally an electrically heatable vessel for a heat fluid and a valve controllable by electronic closed-loop control and/or a flow drive controllable by electronic closed-loop control for the charging of the workpieces with heat fluid; and 
 an electronic controller having a control program, where the fluid drive for the cooling fluid, the temperature sensors, the optional heating elements, the optional valve and the optional flow drive for the heat fluid are connected to the electronic controller; 
   wherein the quench apparatus is designed and set up to cool down the workpieces such that an average temperature T(t) of the workpieces has a progression against time according to the relationship   
       
         
           
             
               
                 T 
                 ⁡ 
                 ( 
                 t 
                 ) 
               
               = 
               
                 
                   T 
                   0 
                 
                 + 
                 
                   
                     T 
                     1 
                   
                   [ 
                   
                     1 
                     + 
                     
                       tanh 
                       ⁡ 
                       ( 
                       
                         - 
                         
                           t 
                           τ 
                         
                       
                       ) 
                     
                   
                   ] 
                 
               
             
           
         
         where t denotes time in seconds, 150° C.≤T 0 ≤250° C., 600° C.≤T 1 ≤820° C., 12 s≤τ≤24 s, 0 s≤t≤Γ and 180 s≤Γ≤240 s. 
       
     
     
         11 . The system as claimed in  claim 10 , wherein said system comprises one or more tempering bodies, and the at least one tempering body
 takes the form of a cylinder or cuboid;   takes the form of a tube having a circular or rectangular opening cross section;   takes the form of a box having a multitude of compartments in shaft form for the accommodation of workpieces; or   takes the form of a box having a base plate and four side walls and comprises multiple movable dividing walls.   
     
     
         12 . The system as claimed in  claim 10 , wherein the at least one heating element takes the form of an infrared lamp. 
     
     
         13 . The system as claimed in  claim 10 , wherein the quench apparatus is equipped with an infrared sensor or pyrometer, and a viewing field of the infrared sensor comprises a defined region of the quench volume V and a batch carrier disposed therein. 
     
     
         14 . The system as claimed in  claim 10 , wherein the quench apparatus is equipped with an infrared camera for the measurement of the temperature of the workpieces. 
     
     
         15 . The system as claimed in  claim 10 , wherein the control program is designed and set up to control the fluid drive for the cooling fluid, the heating elements, the valve and/or the flow drive for the heat fluid depending on an average temperature of the workpieces or a temperature of a metallic reference body according to a closed-loop control algorithm.